The invention relates to a voltage generator intended to be controlled by a control signal which comprises at least an active part and an inactive part.
The invention also relates to a signal intended to be used for controlling a voltage generator and comprising at least an active part and an inactive part, a circuit for controlling the contrast of a liquid crystal display screen by varying a power supply voltage applied to said screen, and an electronic device comprising a liquid crystal display screen and such a control circuit.
The invention is notably used in the field of telephony for telephone devices with liquid crystal display screens, for example screenphones, mobile phones, etc.
Such a voltage generator is described in U.S. Pat. No. 5,272,614 filed by the applicant on Jul. 2, 1992. This voltage generator particularly comprises a DC converter controlled by a microprocessor. The control signal supplied by this microprocessor to said converter is a pulse width-modulated signal. The output voltage of the converter thus varies with the cyclic ratio of said control signal.
Such a voltage generator behaves quite satisfactorily in the majority of cases. However, it may be insufficient when an output voltage is to be obtained which varies in a very precise way, as is, for example the case when controlling the contrast of a liquid crystal display screen.